Tracking systems are well established within navigation technologies and have to be calibrated before they can produce reliable tracking information. These calibration procedures are usually performed within an idealized set-up to minimize calibration errors. During the intra-operative use of a tracking system, several error sources may occur, e.g. de-calibrations of the tracking volume because of changing physical conditions like heat effects, mechanical distortions of the camera or tracking system, inhomogeneity of physical parameters, such as distortions of electromagnetic fields or different light conditions in the tracking volume, systematic and statistical errors in marker detections, etc. Those de-calibrations may affect the accuracy of the tracking system.
In general, calibration works in a generic way and aims to minimize inaccuracies in the tracking procedure. However, in many cases systematic errors remain in the particular use of the tracking system. A generic calibration procedure is not able to solve the problems resulting from changing circumstances.
On the other hand, individual calibration procedures are quite time consuming and in many cases can only be performed by trained specialists. Thus, it is often not possible to fine-tune the calibration for particular operation cases.